In multiplayer games you can choose a different player’s creature each upkeep. You are forced to pick a creature that some opponent controls if there is at least one creature on the battlefield that is a legal target.

10/4/2004

If you have more than one Djinn, you can have all of them target the same creature with their ability.

10/4/2004

If there are no creatures your opponent controls to target at the beginning of your upkeep, ignore this ability.